Preserving the Fibrous Layer of the Mandibular Condyle Reduces the Risk of Ankylosis in a Sheep Model of Intracapsular Condylar Fracture.

PURPOSE: The aim of this experimental study was to investigate the role of the fibrous layer of the condylar head in the formation of temporomandibular joint (TMJ) ankylosis in a sheep model of intracapsular condylar fracture. MATERIALS AND METHODS: Six growing Xiao-wei Han sheep were used in the study, and bilateral TMJ surgery was performed in each sheep. In the left TMJ, sagittal fracture of the condyle, removal of the fibrous layer of the condylar head, excision of two thirds of the disc, and removal of the fibrous zone of the glenoid fossa were performed. In the right TMJ, the same surgical management was performed, except that in each sheep, the fibrous layer of the condylar head was preserved. Three sheep were killed humanely at 1 month postoperatively, and the other 3 sheep were killed humanely at 3 months postoperatively. The TMJ complexes were examined by histologic evaluation. RESULTS: Fibrous ankylosis was observed on the left side in 3 sheep at 1 month postoperatively and in 2 of 3 sheep at 3 months postoperatively. Fibro-osseous ankylosis was achieved on the left side in 1 sheep at 3 months postoperatively. In the right TMJ, the main postoperative histologic findings included condylar fracture healing, topical rupture or exfoliation of the fibrous layer of the condyle, and fissure between the fibrous layer and the proliferative zone of the condyle. However, no evidence of ankylosis was observed. The TMJ ankylosis scores on the right side were significantly lower than those on the left side at different time points (P < .05). CONCLUSIONS: This study showed that the presence of the fibrous layer of the condylar head prevented the development of TMJ ankylosis in a sheep model of intracapsular condylar fracture.